Silicosis among foundry workers. Implication for the need to revise the OSHA standard

Our plain-English summary of Silicosis among foundry workers. Implication for the need to revise the OSHA standard, by K.D. Rosenman, M.J. Reilly, C. Rice, et al (American Journal of Epidemiology, 1996).

The study

• Authors: K.D. Rosenman, M.J. Reilly, C. Rice, V. Hertzberg, C.Y. Tseng, H.A. Anderson
• Journal: American Journal of Epidemiology
• Published: 1996;144(9):890-900
• Cited by: 71 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

To evaluate the risk of pneumoconiosis among workers in a Midwestern automotive foundry, medical records and silica sand exposure data were analyzed for 1,072 current and retired employees with at least 5 years of employment as of June 1991. Approximately half of these employees had worked at the foundry for 20 or more years. Sixty workers were found to have radiographic evidence of pneumoconiosis. Twenty-eight workers had radiographs consistent with silicosis, of which 25 were consistent with simple silicosis and three with progressive massive fibrosis. The prevalence of radiographic changes consistent with silicosis increased with: number of years worked at the foundry (6% for 20-29 years and 12% for 30 or more years); cigarette smoking (12.2% among smokers with high silica exposure vs. 4.4% among never smokers with high silica exposure); work area within the foundry (cleaning room, core room, mold area, core knockout); and quantitative silica exposure (0.3-2.7% of workers at the current Occupational Safety and Health Administration (OSHA) standard and 4.9-9.9% of workers above the OSHA standard). In addition, the odds of developing radiographic changes consistent with silicosis were increased for African Americans (odds ratio = 2.14, 95% confidence interval 0.85-5.60) in comparison with whites. (The risk was similar when silica exposure was equal, but African-American workers on average had greater exposure to silica, despite having a similar duration of work as white workers.) Another eight workers had radiographic evidence of asbestosis, and 24 had pleural plaques. These asbestos-related changes were not associated with increasing exposure to silica but rather were associated with being in the maintenance department and performing repair work. After controlling for cigarette smoking, race, and exposure to silica at another job besides the foundry, the authors found a 1.45 increased risk of developing a radiograph consistent with silicosis after 20 years of work at the current OSHA standard, and a 2.10 increased risk after 40 years of work at the current OSHA standard. On the basis of these findings, the authors recommend maintaining silica air levels no higher than the exposure level of 0.05 mg/m3 recommended by the National Institute for Occupational Safety and Health.

In plain English

This study reviewed chest X-rays, records and silica sand exposure data for 1,072 current and retired employees of a Midwestern gray iron foundry that made automotive engine blocks. Of 952 readable X-rays, 60 were judged by at least two of three certified readers to show pneumoconiosis. Twenty-eight showed changes consistent with silicosis (25 simple silicosis, three progressive massive fibrosis). Eight showed changes consistent with asbestosis, and 24 showed pleural changes without lung-tissue changes, consistent with asbestos exposure. Silicosis-type changes were more common with longer work (12.0 percent at 30 or more years) and higher silica exposure. They were also associated with smoking and with a history of tuberculosis. The asbestos-related changes were not associated with silica exposure but with maintenance work. In a statistical model that adjusted for smoking, race and silica exposure at other jobs, 40 years at the OSHA silica limit was linked to an odds ratio of 2.10 (95 percent confidence interval 1.56 to 2.82) for silicosis-type changes. The authors concluded that the OSHA standard was not low enough to protect workers. They noted their exposure estimates might be too high.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Study of a cohort of current and retired foundry workers, comparing consensus chest X-ray readings by certified "B" readers with silica exposure estimates reconstructed from historical industrial hygiene data; contingency tables and logistic regression
• Who was studied: 1,072 workers at a Midwestern gray iron foundry producing automotive engine blocks since 1949: 549 current production workers, 497 retired production workers and 26 current salaried former production workers, all with at least 5 years of employment as of June 1991. They were 57.7 percent African-American and 96.8 percent male. 952 had readable chest X-rays.
• Exposure: Silica (quartz) from foundry sand, estimated as cumulative (mg-days/m3) and average (mg/m3) exposure by job and exposure zone, without adjustment for respirator use. Asbestos had been used in curtains, gloves, pipe lagging and boiler covering. No airborne asbestos measurements were found in the records.
• Main results:
  • Among 952 workers with readable chest X-rays, 60 had X-rays read by at least two "B" readers as showing evidence of pneumoconiosis.
  • 28 workers had rounded upper-lobe opacities typical of silicosis: 25 with simple silicosis and three with progressive massive fibrosis.
  • 8 workers had lower-lobe linear opacities typical of asbestosis, and 24 had pleural thickening without lung-tissue changes, consistent with asbestos exposure (described as pleural plaques).
  • X-rays consistent with silicosis were found in 6.1 percent of workers with 20-29 years of work and 12.0 percent of those with 30 or more years.
  • At the OSHA standard the prevalence of X-rays consistent with silicosis was 0.3-2.7 percent. Above the current OSHA standard it was 4.9-9.9 percent.
  • Asbestosis-type changes and pleural plaques were not associated with silica exposure. 4 of 8 workers with asbestosis-type X-rays and 9 of 24 with pleural plaques had worked 50 percent or more of their time in maintenance, compared with none of the workers with silicosis-type X-rays.
  • Controlling for exposure, smoking was associated with silicosis-type X-rays. In the highest cumulative exposure group (over 2,160 mg-days/m3), prevalence was 12.2 percent among 115 smokers and 4.4 percent among 46 nonsmokers.
  • Workers with silicosis-type X-rays had higher odds of tuberculosis than other workers (OR = 6.34, 95 percent CI 1.92-19.73).
  • African-American workers had higher odds of silicosis-type X-rays than white workers (OR = 2.14, 95% CI 0.85-5.60). After controlling for silica exposure, prevalences were similar; African-American workers on average had greater silica exposure.
  • After controlling for pack-years of smoking, race and silica exposure at other jobs, 20 years at the current OSHA standard (0.1 mg/m3) gave an odds ratio of 1.45 (95% CI 1.25-1.68) for silicosis-type X-rays, and 40 years gave 2.10 (95% CI 1.56-2.82). At the NIOSH limit of 0.05 mg/m3 the figures were 1.20 and 1.45.
• The authors' conclusion: The authors concluded that the current OSHA silica standard is not low enough to protect workers against X-ray evidence of silicosis, and recommended keeping silica air levels no higher than the NIOSH limit of 0.05 mg/m3. They concluded that the pleural and lower-lobe linear changes were associated with jobs likely to involve asbestos exposure and were not likely related to silica.
• Limitations the authors state:
  • Exposure indices were developed from incomplete historical data.
  • The year a worker's lungs first showed abnormalities was not known and could have been earlier than the X-ray date, so exposure may be overestimated.
  • Respirator use, which would have reduced exposure, was not included in the exposure estimates.

Topics

Medical terms in this study, explained in our Lexicon: Silicosis, OSHA, Pneumoconiosis, Fibrosis, Odds Ratio, confidence interval, Pleural Plaques.

Related studies

• Asbestos-related x-ray changes in foundry workers — K.D. Rosenman, M.J. Reilly (1998)
• Radiographic evidence of silicosis risk in the diatomaceous earth industry — J.M. Hughes, H. Weill, et al. (1998)
• Respiratory health of workers exposed to metal dusts and foundry fumes in a copper refinery — G. Ostiguy, C. Vaillancourt, et al. (1995)
• Mortality of a cohort of men in a silicosis register: further evidence of an association with lung cancer — T.P. Ng, S.L. Chan, et al. (1990)
• An analysis of violations of Osha's (1987) occupational exposure to benzene standard — P.R. Williams (2014)
• Silicosis and smoking strongly increase lung cancer risk in silica-exposed workers — N. Kurihara, O. Wada (2004)

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